Automatic control switch apparatus



Jan. 14, 1930. T. R. HARRISON AUTOMATIC CONTROL SWITCH APPARATUS Filed June 1924 2 Sheets-Sheet l Jan. 14, 1930. HARRlSON 1,743,774

AUTOMATIC CONTROL S ITCH APPARATUS Filed June 1924 2 Sheets-Sheet 2 Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE THOMAS RANDOLPH HARRISON, F PHILADELIHIA, ZPENN SYLVANIA, ASSIGNOR T0 BROWN INSTRUMENT COMPANY, OF PHILADELPHIA, PENNSYLVKNIA, A CORPORA- TION OF I ENNSYLVANIA AUTOMATIC CONTROL SWITCH APPARATUS Application filed June 4, 1924. Serial No. 717,902.

The present invention relates to improvements in apparatus for automatic control systems.

v More particularly the invention relates to apparatus for controlling recorders, switches,

motors, valves, rheostats and like devices in response to mechanical, chemical, electrical or other physical conditions in order to effect a record of the changes, or to maintain predetermined conditions at controlled points.

The present invention comprises improvements in the apparatus disclosed in copending application, Serial Number 7 01,829, filed March 25,1924, in which improved contactin'g galvanometer and control arrangements are disclosed. -In the copending case the contactin'g galvanometer arrangements control a pair of light contacts, which in turn control a set of electromagnetic switches through 'relaying circuit arrangements. The electro- I magnetic switches in turn, control reversing motors which may be utilized to operate scale weights and like devices for automatic control purposes.

An object of the present invention is the provision of contacting galvanometer arrangements in which the electromagnetic switches are eliminated and the control contacts are directly and mechanically controlled by the contacting galvanometer.

' Another object of the invention is the provision of mechanicallycontrolled-contacts of rugged construction with which relatively heavy currents may be handled without sticking thereof, and without destructive arcing.

A further object of the invention is toprovide simplified, more efiicient and more reliable contactinggalvanometer arrangements than have been heretofore available. I Other objects of the invention will appear in the following detailed description of pre' ferred embodiments thereof, of which- Fig. 1 is a perspective view showing a preferred form of the invention? I Fig.2 is a side view showing a modification of the form shown in Fig. 1.

Fig. 3 is a'perspective view showing another form of the invention. I

Fig. 4 is a perspective view showing still I another form.

Fig. 5 is a side view showing a modification of the form shown in Fig. 4. I

Referring to Fig. 1, a shaft 1 is driven at a uniform rate by a suitable motor not shown, and has mounted thereon a cam 2. -An actuating member 3, pivoted at 4 to a suitable fixed support 5 has secured thereto an actuating pin 6which is normally forced against the surface of cam 2 by means of'a spring 7 secured to and urging member3 upward. Pivotally se- 50 cured to the free endof mem ber 3 by pin -8 is a pair of substantially vertlcal connecting links 9. At the upper ends of links 9, shoulders 10 are formed which are adapted to hook over projecting pins 11 which in turn are se- 5 cured to frame 12. Frame 12 is pivotally supported at 13 from fixed support-14 and normally tends to move upward under influence of springs 15 until the forward upper edge engages fixed stop 16. The lower front edges 17 of frame 11 are formed in a shallow inverted V-shape. Pivotallysecured to links 9 by spindle 18 is a member19'which extends to the right in Fig. 1 and acts as a spacer between links 9. 'It will be'noted that spindle 18 and the end of member 19, join links 9 together for movement about pin 8 as a pivot under influence of light springs 23. The free end of 19 rests on a surface 20 and is held against a shoulder 21 of a fixed stop 22 by the 9' action of springs. 23. Pivotally mounted on a spindle 24 supported from a fixed support 25 is apair of contact carrying members 26 and 27 provided with extensions 28 and 29 which are positioned beneath and adapted to 35 I en age member 19. I

ontact carrying members'26 and 27 are forced downward by relatively heavy fiat springs30 and 31 secured at one end thereto and secured at their other ends to fixed support 22. Secured near the outer ends of members 26 and 27 are-latch projections'32 and 33 shouldered and positioned to be engaged by shoulders 34 and 35'of pivoted bell crank members 36 and 37. Members 36 and 37 are pivotally mounted on a fixed-supporting spin -dle 38 I and are, normally urge towards a v fixed stop 39 by springs 40 and 41. Secured" to the bell cranks are actuating bars or extensions 42 and 43. Extensions 42 and 43 are has secured thereto a needle or pointer 46 'whidh' in normal' or undeflected position of the galvanometer, extends immediately below v der formedby the projection 52 or 53 will contacts 47 and 49 the apex of the V-shaped notch formed by surfaces 17 in the front piece of frame '12, and immediately tween the inner ends of extensions 42 and 43. The arrangement is such that when the galvanometer is deflected'the needle 46 tioned over one or the other of extensions 42 and 43.

Secured to members 26 and-27 are rela tively large contacts 47 and 48, which coact with adjustable-contacts 49 and 50 mounted in fixed bar or support 51. Formed on links 9 are disengaging projections 52 and 53 so shaped and positioned that with the parts as shown in Fig. 1, the shoulders formed thereby will clear the ends of members 26 and 27 as links 9move vertically under the influence of cam 2 and springs 7- and 15.

en member 26 or 27 is released, to close the contacts controlled thereby, the arrangement is such that extension 28 or 29 willkick the end of 19 off shoulder 21, and springs 23 will then force members 9'to the right until projection '52 or 53 engages the end of'the corresponding member 26'or 27. The free end of member 19 will rest on shoulder 54 of stop 22 this position of parts, and the initial movement of the upper ends of links 9'willbesuflicient to disengage shoulders 10 from pins 11. Frame 12 will then move upward under influence, of springs 15 until it engages stop 16. 9 approach the bottom of their vertical movement, the shoulslip under the end of the released one of members 26 or 27.' Immediatelythereafter pm 6 will drop ofl the shoulder on cam 2 under the influence of spring 7, and member 3 together with. links 9 will move suddenly upward carrying the free end of the released member 26 or 27 upward and separating the or 48 and 50. AS soon as. frame.12 is released and moves upward the bell crank 36 or 37 which has been actuated will move into engagement with stop 39 under the influence of spring 40 01*.41. On the upward movement of parts, tion 32 or 33 willengage the end of the actuated-bell crank and will cam the lower end thereof to the left againstthe tension ofthe spring 40 or ll individual thereto.

. As the shoulder 32 or 33 passes by shoulder 34 or 35 of hell crank 36 or 37, spring 40 or 41 will urge the lower end of the actuated bell crank to the right latching the actuated above the central space beis -posi-- vertically, in

the influence shoulders 10 will be held hooked over pins the projec- 55 secured thereto into engagement with fixed member 56. This causes a flexing of spring 55 and tends to force links 9 to the left about pivot 8 against the tension of springs 23.

The initial flexing of spring 55 will shift,

surfaces 57 of links 9 against pins 11, and as or just before the upward movement of llnks 9 is completed, shoulders 10 will slide over and engage pins 11, the end of member s 19 will re-engage surface 21 of stop 22, and the parts will assume, the position shown in Fig. 1.

In practice, the galvanometer'44-is connected by conductors 58 and 59 to a suitable control circuit, and contacts 47 to 50 are connected to circuits controlling suitable motors, rheostats, switches or like devices. In applying the arrangement to the recorder circuits as shown in the above'mentioned copending application, the contacting galvanometer and electromagnetic switches there shown are removed,'and leads 58 and 59 of the galva-,

nometer coil '44 shown herein are connected directly to leads 60 and 62'of, the copending case. With the switches of the 'copending case removed, contacts 49 and 50 of the presentarrangement are connected to the'line conductor L and contacts 47 and 48are connected to the conductors 58and 59 of the copending case.

In operation, shaft 1 rotates continuously.

-Under the influence of'cam and springs 7 and I 15, links 9 and frame 12 are given a downward' movement until shoulder, and the throw the So long as no deflection of the galvanometer needle occurs, members 26 and 27 will be latched in the position shown in Fig. 1, and member 19 will rock 011 stop 22 as links 9 move pin 6 drops off the cam ment of links 9 to the right about pin 8 under of springs 23. In this manner 11 of frame 12. Under these conditions, ppinter 46 will pass downward between the ends of extensions 42 and 43, as the frame lowers. Upon a deflection of the galvanom--' eter needle, due to an unbalance caused by the conditions to be controlled .or measured, pointer 46 will be positioned over one or'the springs 7 and 15 operate to. frame and links suddenly upward.

this manner preventing move-- other of the extensions 42 or 43. As the frame is lowered, pointer 46 will rock down-' ward and engage the extension42 or 43 over which it is positioned and continued downward motion of frame will force the latching arm of the corresponding bell crank 36 or 37 to the left in Fig. 1, until the correspond ng 1 member 26 or 27 is freed to move under the influence of its spring 30 or 31. The released member 26 or 27 will snap downward causing contact 47 or 48 to engage contact 49 or 50 as the case maybe, with a blow which insures thereof oii shoulder 21 of stop 22. Links .9

y will then move to the right under influence of springs 23 until projection 52 or 53 engages the tripped member 26 or 27 As above set forth, this movement of links 9 about pivot 8 will disengage shoulders 10 from pins 11, permitting frame 12 to move upward against stop 16. The upward movement of the frame immediately frees the galvanometer needle 46 so that a new position may be assumed thereby. Links 9 willqcontinue to move downward until just before pin 6 drops off the c am shoulder at whichpoint the shoulder formed by projection 52 or 53 will slip under the end of the tripped member 26 or 27. When pin 6 drops ofi the cam shoulder, spring 7 will snap links 9 and the actuated one of members 26 or 27 upward, causing a sudden disengagement of contacts 47 and 49 or 48 and 50, latchingthe actuated member 26 or 27 in the position shown in Fig. 1, and finally hooking shoulders 0 over pins 11 as above set x forth. The sudden interruption of the contacts reduces sticking and arcing of the contacts. The contacts may be made of sufiicient size to remain cool in operation so that any are on interruption will be rapidly .extinguished. 'Any common and well known expedient for preventing arcing, as for example a condenser connected across the contacts, may be utilized when highly inductive circuits are to be interrupted. -With shoulders 10 hooked over pin 11, the cycle of operations is complete, and succeeding cycles may proceed.

Owing to the inclination of surfaces 17 of frame 12, it will be clear that the point in the downward movement of frame 12 at which the contacts will be tripped will vary with the degree of deflection of'the pointer.

' As the point of interruption of the actuated ico contacts is definitely fixed in the cycle, the time interval during which the'contacts will be closed varies directly with the degree of deflection. It will, however, be obvious that the same effect may be attained by mak Eng the frame.

lower front edge of frame 12 straight and inclining the upper edges of extensions 42 and 43 at suitable angles with relation the The form shown in Fig. 1 is especially adapted for quick acting sensitive arrangements, because of the fact that the galvanometer needle is freed to assume a new position in accordance with changed conditions as soon as either contact is tripped. For slower acting arrangements where there is no need for freeing the needle or pointer 46 im tended to project into the path of vertical movement of projections 52 and 53 on links 9. The shape of cam 2 and the proportions of parts are such that the shoulders formed by projections 52 and 53 will drop sufficiently to permit engagement of contacts47 and 49, and 48 and 50 before member 26 or 27 is tri ped.

n operation, with the galvanometer undeflected, pointer 46 will pass between the ends of extensions '42 and 43, and contacts 48 and 49 will remain latched u When a deflection occurs, the downwar movement of links 9 will drop projections 52 and 53, then one or the other of the bell cranks 36 or 37 will be actuated to release the corresponding contact member 26 or 27 The contacts will re main closed and pointer 46 will be engaged by frame 12 until pin 6 dro. s off, the shoulmay assume a new position, and the'cycle of A operations may be repeated. A full understanding of this form will be had by referring to the disclosure set forth for Fig. 1

A modified arrangement for accomplishing the functions. and operations set forth in connection with Fig. 1 is shown in Fig. 3. Pivoted to supporting spindle 13 of frame 12 is an actuatin structure comprised of links and 61 whic at their lower end have a toe 62 securedthereto. The end of toe 62 is held against cam 2 by means of spring 63. Frame 12 has extensions 64 and 65 formed integrally therewith which extend in forward and downward manner and have rigidly secured between the ends thereof an actuating extension 66. A spring 67 secured to exten sion 66 at one end and to a suitable fixed support at the other end urges the lower end of connected by means of pin 70 tolinks 60 and 61. A flat spring 71, secured to an extension 72 of member 69 is adapted to engage extension 66 and will force member 68 into the position shown in Fig. 3, when frame 12 is against stop 16 and toe 62 is against the low 78 and tend to move to the right'under the influence of springs 79 and 80. Mounted respectively on bell cranks 76 and 77 are contacts 47 and 48, arranged to coact with conone of the bell cranksto' latched position v 85 tacts 49 and'50 mounted on block 51.

Contacts 47 to 50 are held in disengaged position by means of latch members 81 and82 pivoted on fixed spindle 83 and the inner ends of which 'are held in engagement with shoulders 84 and 85 of bellcranks 76 and 77 by the action of springs 79, 80, 86 and 87.

M6unted on the outer ends of latches 82 and 83 are'trip bars 42 and 43, which as set forth in connection withFigs 1 and 2, are positioned beneath and within the front end of frame 12, with their inner ends separated to permit downward movement of galvanometer pointer 46 in'central or balanced position without engagin either as-frame 12 rocks the pointer-downward. Formed integrally with member 69 is a contact restoring extension 88 which is positioned and adapted to engage projections 89 and 90 of hell cranks 76 and 77, to interrupt the contacts47 and 49, or 48 and 50, and to restore the actuated when toe 62 drops olf the shoulder of cam 2 underinfluence of spring 63.

- In operation of this form, a rocking mo tion is imparted by cam 2 and spring 63 to toe 62 which in turn produces an oscillating movement of member 69 about 13 as a pivot. Movement of 69 is imparted to member 66 by shoulder 68, and in this manner frame 12 is rocked vertically about pivot 13 against the tension of spring 67 So long as pointer 46, is undeflected, no other eflectvwill be produce'd. When the galvanometer is deflected however, pointer 46 will be positioned over bar 42'or 43, and at a point in the descent of the frame depending upon the degree of deflection, member .80 or 81 as the case may be, will be actuated to disengage the end thereof from shoulder 84 or 85 of bell crank 7 6.or 77. The released bell crank willthen .snap for- ,ward under the'infiuence of its spring 79 or 80 causing projection 74 or 75 to engage exten-- sion 73 of member 69, forcing it downward,

and finally causing engagement of contacts 47 and 49, or 48 and 50 with an impact. The downward movement of member 69 removes shoulder 68- thereof from engagement with the end of member 66, andmember 66 toi gether with frame 12 engages stop 16. The

upward movement of the frame frees pointer 46 so 'that-a new deflected, position may be imm'e'dlate'ly assumed thereby'l}; The arrangeand 106 which ate positioned 2. When this occurs spring 63 will move the I actuating frame together with member 69' suddenlyv to the right in Fig. 3. This movement of 69 will cause 88 to force the actuated bell crank 76 or 77 upward about pivot 78, causing a sudden interruption of the engaged contacts, and moving the upper arm of the actuated bell'crank to the left-until the end .of latch 81 or'82 drops back of shoulder 84 or 85 under thev influence of spring 86 or 87 and latches the .bell cranks in unactuated position as shown in Fig. 3. After the latching is effected, due 'tothe flexing of spring 71 in engagement with 66, surface 91 of member 69 will be forced into engagement with the end of member 66 until shoulder 68 slips over the edge of and re-engages the end of 66 at or just before the "limit of movement of toe 62 to the right into engagement with the low point of cam 2. A suitable fixed stop 90 may be provided to limit the downward movement of member. 69.

The application of this form tothe recorder arrangement of the copending case is the same as set forth above for the connection ofthe form shown in Fig. 1, and the same functions and advantages are attained as are set forth in the description'of Fig. 1. In Fig. 4, a form of-the invention is shown in which all of the contacts are movable." In this form, links 9 are permanently connected to pins 11 of frame 12 and the frame is" rocked about pivots 13 under the influence of cam 2 and spring 7. Downward movement of frame 12 with the galvanometer 44 debers to snap to the left about fixed pivot 94 under influence of spring 95 M96, bringing contact 47 or 48 into engagement with con-.

tact 49 or 50, as the case may be. Springs 95 and 96 are'secured to fixed supports 97 and 98. Contacts 49 and 50 are mounted on a bar 99 supported froma bar 100 which-in turn is pivotally mounted on spindle 94 and acts as a spacer between members 92 and 93. A spring 101 secured to fixed support 1'02, forces member 99 to the left into engagement with a cam 103 mounted on'a shaft 104. Shaft .104 is driven at thesame speed as shaft 1 and in definitely fixed relation with respect thereto by suitable drive connections, not shown) Secured to cam 103 are projecting pins 105 to engage surfaces 107 and 108 ofmembers 92 and 93 when these members are tripped, and to restore flected will cause pointer 46 to engage one or cycle.

In operation, member 92 or 93 will be tripped at a point inthe downward move-- ment of frame 12 depending upon the degree of deflection of the galvanometer, and one or the other set of contacts 47 and 49, or 48 and 50 will close with a blow. The parts are positioned and proportioned so that the tripped contacts will remain in engagement until member 99 drops off the shoulder of cam 103.

At this point the engaged contacts will move together to the left in Fig. 4 until surface 107 or 108 of the tripped member 92 or 93 engages pin 105 or 106 when the movement of bar 99 will continue until the low point of the cam is reached, and the movement of 92 or 93 will be arrested. This effects a sudden interruption of the engaged contacts. Further movement of.pin 107 or 108 will then immediately cam the lower end of the tripped member 92 or 93 to the right and will shift the upper end thereof to the left until latch 81 or 82 drops behind the latching shoulder under influence of spring 86 or 87 and locks the contacts in open position. During the restoration of the contacts to latched position,. cam 2 permits the upward movement of frame 12. The parts are then in-position for a succeeding cycle of operations. d

It will be noted that the gal-vanometer needle is not freed in Fig. 4 until the normal upward movement of frame 12 occurs. Freeing of the needle as soon as the contacts are tripped-may be effected as shown in'Fig. 5.

The cam 2 and spring 7 are positioned on the bottom of member 3 so that the downward movement of frame 12 is spring actuated, and the upward movement thereof is cam actuated. Secured to frame 12 is a magnetizable crossbar or armature 109 which is, positioned to be attracted by energization of an electromagnet 110 secured to a suitable fixed support, not shown. Magnet 110 may be energized through circuit comprisin conductor 111, a source of electrical energy 12, contact spring 113, contacts 114 and 115, and conductor 116. Contacts 114 and 115 are positioned so that when either member 92 or 93 istripped.

andcauses engagement of the contacts 47 and 49, or'48 and50, an extension 117 provided on each member 92 and 93, willifo'rce contact 114 into engagement with 115. Magnet 110 will be energized, raising frame 12 upward into engagement with stop 16, and pointer 46. will be freed to assume a new'position. Magnet 110 will remain energized until the ripped member 92 or 93 is restored by pin 105 or.106 as set forth in connection with Fig. 4, when extension -117 will move away from contactspring. 113 and will permit contacts 114 and a 115 to separate, effecting de-energization of magnet 110. In this manner as soon as one or the other of the sets of contacts is tripped, frame 12 will be raised to free-the pointer.

from the spirit of the invention.

Accordingly, what .is desired to be secured by Letters Patent and claimed as new is:

1. Automatic control apparatus comprising a galvanometerand pointer therefor, periodically operating means adapted to actuate said pointer when deflected from its normal position, a plurality of sets of contacts, actuating springs for causing engagement of said contacts, and solely mechanical means between said pointer and said contacts for controlling the engagement thereof.'

2. Automatic control apparatus comprising a contacting galvanometer, mechanical operating means coacting with said galvanometer and a plurality of spring closed contacts mechanically controlled by the coaction of said galvanometer and said operating IDES/11S.

3. Control apparatus comprising in combination, a pair of contacts, a latch for maintaining said contacts indisengaged position,

a -galvanometer pointer adapted to mechanically actuate said latch, and cyclically operating means for said galvanometer pointer.

' 4. Control apparatus comprising in combination, a plurality of pairs of contacts, solely mechanical means, individual to each pa r of contacts to maintain the same in sefparated position, a galvanometer, a pointer or said galvanometer adapted to directly actuate said "a galvanometer, mechanical means controlled by said galvanometer for actuating aplurality of contacts variably in accordance with the deflection of said galvanometer, and solely mechanical means independent of said galvanometer for invariably restoring are actuated ones of said contacts.

6. Automatic control apparatus comprising a galvanometer, mechanical means operating in cycles and coacting with said galvanometer,='means actuated at different points in the cycles of operation of said mechanical means in a manner dependent upon the amount of deflection of said galvanometer, and solely mechanical means for restorin said actuated means at the same point in eac cycle.

7. Controlapparatus comprisinga contact ing galvanometer, periodically operating mechanical means coacting with said galvanometer, a plurality of contacts caused to move into. engagement by the coaction of said gal- 10 vanometer and said mechanical means, and

spring actuated means for suddenly interrupti li glg'l said engaged contacts.

e combination as set forth in claim 6- in which said last mentioned means comprises spring actuated means for effecting a quick restoringimovement of said actuated means.'

9. In combination, a set of contacts; means for latching said contacts in disengaged position; a galvanometer; cyclically operating means coacting with said galvanometer to trip said latching means and permit engagement of said contacts; and solely mechanical l means for restoring said tripped contacts to latched position.

a'ted to restore said contacts at a predetermined point in'the cycle of operations of said operating means. I

11.- The combination as set forth in claim 9 in which said last mentioned means comprises a spring operative to suddenly disengage said tripped contacts at a predetermined point in the cycle of operationsof said operating means.

tion; a galvanometer comprising a, pointer.

adapted to engagelsaid releasing means; and operatingmeans for forcing said pointer into engagement with said releasing means; and means actuated by the movement of said members -to actuated position to free said operat- 5 ing means from engagement-with said galvanometer needle.

I 15;. The combination as set forthinclaim 13 in which said last .mentioned means is solelyand entirely mechanical.

1 5..In combination, a galvanometer; a pointer for said galvanometer; actuating means for said pointer; operating means of .said actuatingmeans; releasable connection between said operating means and said actu ating means; a controlling trip for said releasable connection; releasing trips actuated by said pointer; and spring actuated members controlled by said releasing trips; said spring actuated members being operative to actuate 10. The combination as set forth in claim 9 i in which said last mentioned means is oper-- said controlling trip to efiect disengagement of said actuating means and said pointer.

16. Control apparatus comprising a pair of contacts, a, galvanometer, a source of stored energy, periodically operating means controlled by said galvanometer for releasing said energy to operate said contacts and means for periodically storing said energy.

17 Control apparatus comprising a pair of contacts, a galvanometer, means controlled by said galvanometer for closing said contacts with a snap action and means for thereafter opening said contactswith a snap action.

18. Control apparatus comprising a con-' tact member, a second contact. member normally latched ing-disengaged position from of contacts, a latch device for normally maintaining said contacts in disengaged position, a galvanometer and periodically operating meansl'co-operating with said g'alvanometer for operating said latch device to release said contacts toengagement.

21. Control apparatus comprising a pair of contacts, a latch device for. maintaining said contacts in disengagement, means for periodically operating said device torelease one of said contacts to engage the other contact, and a second device for operating said onecontact to engage with said latch device operated by said first mentioned means.

22. Control apparatus comprising a pair of contacts, a latch device for maintaining said contacts in disengagement, means responsive to a predetermined condition in operating said device to release one of said contacts to engage the other contact, a second.

device for operating said contact to en age said latch device periodically controlled said first mentioned means, said first and second device being normally ineflective to per-' form any operation during said periodic conditioning.

23. Control apparatus comprising ,afpair of contacts,- a spring forcing said contacts to engage a latch device for maintaining said contacts in isengagement, periodically oper ating mean anda galvanometer includingja deflecting member cooperatin when in deflected position with said perio ic means during its periodic operation for operating said -means periodically conditioned for operating said latch device and a galvanometer coacting with said last mentioned means for operating said latch device to release said members; I

26. Control apparatus comprising a ,plurality of members normally latched in disengagement, periodically operating means for releasing said members from latched position, said means being normally ineifective and means operative following the release of said members to operate said member into latched engagement.

27. Control apparatus comprising a memher, a latch device for maintaining said member in latched position, means for operating said latch device for releasing said member, second means for operating said first mentioned means, said second means being also operative to operate said member to'latched position.

28. Control apparatus comprising a pair of contacts, a galvanometer, means responsive to the movementof said galvanometer for closing said contacts with a snap action, and means operative following the closing of said contacts for releasing said galvanometer.

29. Control apparatus comprising a pair of contacts, means for normally latching said contacts in disengaged position, a galvanoineter, a periodically operating member engaging said galvanometer for operating said latch member to release said contacts for engagement, and means operative uponthe closing of said contacts for disengaging said periodically operating means from said galvanometer.

30. Control apparatus comprising a pair of contacts, a latch device for maintaining said contacts in disengaged position, a galvanometer, a member periodically engaging said galvanometer for operating said latch device to release said contacts, said periodically operating member being 50 positioned as to engage said galvanometer at various positions of its movement in accordance with the angular swing of said galvanometer.

- 31. Control apparatus comprising. a pair of contacts,a galvanometer, a pointer, a periodic member, means controlled by said pointer and operated by said periodic member for conditioning said contacts for engagement and means for operating said conditioned contacts 1nto engagement with a snap action.

In testimony whereof, I affix my signature.

THOMAS RANDOLPH HARRISON. 

